Castle marketed films for which Universal owned the rights, so both GORILLA AT LARGE (20th) and KILLER APE (Columbia) are out-of-the-running. If it's not a newsreel/docudrama, then the possibilities are limited. THE MONSTER AND THE GIRL, perhaps?

‘Killer Gorilla’ (1952) 10m, prod. United World/Castle Films. Many nature treatments derived from notoriously inaccurate adventure travelogues. ‘Killer’ is a particularly odious example, focusing on a gorilla hunt culminating in the "killing" of an ape that had already been dead for several days, its belly ripped open from port to starboard. If its fly-encrusted mouth could have spoken, it might have told of the awful job its porters must have had, lugging its carcass from one spot to another for camera set-ups, as it heated up under the stifling Congo sun.